Method and system for use with an integrated gasification combined cycle plant

ABSTRACT

An integrated gasification combined cycle (IGCC) power plant includes an air separation unit configured to discharge a nitrogen flow and an oxygen flow. A first heat exchanger is attached to the air separation unit and heats the discharged nitrogen flow. A second heat exchanger is attached to the air separation unit and heats the discharged oxygen flow. A third heat exchanger is attached to a steam cycle of the IGCC and heats a condensate stream received from the steam cycle. A first adiabatic air compressor is attached to the first, second, and third heat exchangers. The adiabatic air compressor is configured to discharge a compressed air flow comprising a first flow and a second flow. The first flow is channeled to the first and third heat exchangers, and the second flow is channeled to the second and third heat exchangers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/470,538 filed May 22, 2009, which is hereby incorporated by referencein its entirety.

BACKGROUND OF THE INVENTION

The field of the invention relates generally to an integratedgasification combined cycle (IGCC) system, and more particularly, to anIGCC system that includes an adiabatic axial air compressor.

In at least some known IGCC power plants, hydrocarbonaceous feeds,including low value feeds, are reacted with high purity oxygen, such asapproximately 95% oxygen purity, to produce combustion products,including syngas, at a temperature of about 2200° F. to about 2700° F.The resulting syngas is combusted within a combustion turbine to produceelectric power.

Moreover, in at least some known IGCC power plants, the oxygen issupplied by an air separation unit (ASU). More specifically, to supplythe oxygen from the ASU, air supplied to the ASU is initially compressedusing an intercooled air compressor. However, within known intercooledair compressors, thermal energy from each stage of cooling istransferred to cooling water rather than being used within the powerplant. Such thermal energy is transferred rather than used within theplant because the thermal energy within the intercooled air compressoris generally below about 200° F. Moreover, the transfer of the thermalenergy to the cooling tower requires additional power consumption by thecooling water circuit. Accordingly, a need exists for an IGCC powerplant with improved heat efficiency. The embodiments described hereinseek to improve the heat efficiency of an IGCC power plant.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a method of operating an integrated gasificationcombined cycle power generation system is provided. The method includescompressing air in an adiabatic air compressor to produce a compressedheated air stream, heating a nitrogen stream using the compressed heatedair stream to produce a heated nitrogen stream and a cooled compressedair stream, and channeling the cooled compressed air stream to an airseparation unit.

In another embodiment, a integrated gasification combined cycle (IGCC)power plant is provided. The IGCC power plant includes a first heatexchanger configured to generate steam, an air separation unitconfigured to discharge a nitrogen flow and an oxygen flow, and a secondheat exchanger coupled in flow communication with the air separationunit. The second heat exchanger is configured to heat the dischargednitrogen flow. The IGCC power plant also includes a first adiabatic aircompressor coupled in flow communication with the first and second heatexchangers. The first adiabatic air compressor is configured todischarge a compressed heated air flow including a first flow and asecond flow, wherein the first flow is channeled to the first heatexchanger and the second flow is channeled to the second heat exchanger.

In yet another embodiment, a steam generation system is provided. Thesystem includes a first adiabatic air compressor for generating a firstcompressed air flow, a second adiabatic air compressor for generating asecond compressed air flow, and a steam generator coupled in flowcommunication with the first adiabatic air compressor and the secondadiabatic air compressor. The first and second compressed air flowsgenerate steam within the steam generator.

The embodiments described herein provide a process and a system for usein operating an integrated gasification combined cycle (IGCC) powergeneration plant with improved thermal efficiency, as compared to knownprocesses and/or systems for operating an IGCC power plant. Using anadiabatic air compressor to produce a stream of compressed heated air,and to heat a stream of nitrogen, as described herein, facilitatesreducing overall power consumption of the IGCC power plant by increasingthe thermal efficiency of the plant. More specifically, the systems andprocesses described herein use an adiabatic air compressor to capturehigh level heat generated within the IGCC power plant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an exemplary integrated gasificationcombined cycle (IGCC) power generation plant.

DETAILED DESCRIPTION OF THE INVENTION

The methods and systems described herein include an adiabatic aircompressor for supplying air to an air separation unit. The adiabaticair compressor generates a compressed heated air flow from which thermalenergy is recovered within an integrated gasification combined cyclepower generation plant. More specifically, in the exemplary embodiment,the compressed, heated air flow is used to heat a diluent nitrogen flowand to produce a medium pressure steam. As such, although an adiabaticair compressor consumes more power than known intercooled aircompressors, the thermal energy of the adiabatically compressed air maybe recovered, rather than rejected through a cooling tower. Accordingly,the method and system described herein improves overall efficiency of anintegrated gasification combined cycle power generation plant ascompared to integrated gasification combined cycle power generationplants that use an intercooled air compressor to supply air to an airseparation unit.

FIG. 1 illustrates a schematic view of an exemplary integratedgasification combined cycle (IGCC) power generation plant 10 (alsoreferred to herein as “power plant” or “plant”). In the exemplaryembodiment, plant 10 includes a gas turbine engine 12, a steam turbine14, a gasification unit 16, and an air separation unit (ASU) 18. Gasturbine engine 12 includes a compressor 20, a combustor 22, and aturbine 24. In the exemplary embodiment, compressor 20 is an adiabaticaxial flow type compressor, and turbine 24 is coupled in flowcommunication with a heat recovery steam generator (HRSG) 26, whichsupplies steam to steam turbine 14. HRSG 26 and steam turbine 14 areconsidered to be a steam cycle. Gasification unit 16 is coupled in flowcommunication with ASU 18 and combustor 22.

Plant 10 also includes a nitrogen compressor 28, an adiabatic aircompressor 30, a first heat exchanger 32, a second heat exchanger 34 athird heat exchanger 36, and a fourth heat exchanger 38. In analternative embodiment, plant 10 does not include third heat exchanger36 and/or fourth heat exchanger 38. In the exemplary embodiment,nitrogen compressor 28 may be a single or multi-stage intercooledcompressor, and adiabatic air compressor 30 is an adiabatic axial aircompressor. Alternatively, compressor 28 and/or compressor 30 may be anysuitable compressor that enables plant 10 to function as describedherein.

In the exemplary embodiment, nitrogen compressor 28 is coupled in flowcommunication with ASU 18 and first heat exchanger 32, adiabatic aircompressor 30 is coupled in flow communication with ambient, first heatexchanger 32, and second heat exchanger 34. First heat exchanger 32 iscoupled in flow communication with nitrogen compressor 28, adiabatic aircompressor 30, gas turbine engine compressor 20, combustor 22, andfourth heat exchanger 38. In an alternative embodiment, first heatexchanger 32 is not in flow communication with gas turbine enginecompressor 20. In the exemplary embodiment, second heat exchanger 34 iscoupled in flow communication with adiabatic air compressor 30, gasturbine engine compressor 20, the steam turbine cycle, and thirdexchanger 36. Third heat exchanger 36 is coupled in flow communicationwith ASU 18, gasification unit 16, second heat exchanger 34, and fourthheat exchanger 38. In an alternative embodiment, rather than being inflow communication with ASU 18 and/or gasification unit 16, third heatexchanger 36 is coupled in flow communication with a water source and/orsteam source. In the exemplary embodiment, fourth heat exchanger 38 iscoupled in flow communication with first heat exchanger 32, third heatexchanger 36, ASU 18, and the steam cycle.

During operation of plant 10, air 40 from ambient enters adiabatic aircompressor 30 and is compressed therein. More specifically, in theexemplary embodiment, air 40 is compressed to a pressure of at least 180pounds per square inch gauge (psig), more particularly, is compressedwithin a range of about 180 psig to about 250 psig. Air 40 is alsoheated during the compression process to a temperature in a range ofabout 750° F. to about 850° F. As used herein, a fluid described herein,such as air, nitrogen, and/or oxygen, is considered to be a fluid flowand/or fluid stream, and the terms “flow” and “stream” are usedinterchangeable herein.

Air 40 is also channeled from the ambient into gas turbine enginecompressor 20 for compression therein. Because compressor 20 is also anadiabatic compressor, compressed air 44 discharged from compressor 20has similar characteristics, such as pressure and temperature, ascompressed air 42 discharged from compressor 30, as described above. Assuch, when air 46 is extracted from compressed air 44 and channeled fromcompressor 20 to ASU 18, characteristics of extracted air 46 andcompressed air 42 may be controlled such that the two air streams haveapproximately equal pressures and temperatures. For example, extractionair 46 may have a pressure within a range about 2 to about 15 pounds persquare inch (psi) of compressed air 42. In an alternative embodiment,air 40 is pre-processed, depending on ambient conditions, beforeentering compressor 20.

In the exemplary embodiment, compressed air 44 is channeled to combustor22 for use in combusting air 44 and fuel, such as syngas 48, therein.Combustion gases 50 are channeled into turbine 24 for generating power,and are discharged from turbine 24 into HRSG 26 to generate steam 52.Steam 52 generated is channeled through steam turbine 14 to generatepower.

Extraction air 46 and compressed air 42 are mixed to form a hot, highpressure (HP) air stream 54. Alternatively, air is not extracted fromcompressed air 44 to form extraction air 46, and only compressed air 42is channeled to ASU 18. In the exemplary embodiment, HP air stream 54 ischanneled to ASU 18 via at least first heat exchanger 32 to generate acooled HP air stream 56. Further, in the exemplary embodiment, HP airstream 54 is also channeled through heat exchangers 34, 36, and/or 38 toutilize thermal energy in HP air stream 54 after stream 54 heats diluentnitrogen (N₂) 58, as described in more detail below. More specifically,HP air stream 54 may have enough thermal energy to heat diluent N₂ 58and at least one other fluid flow. As such, HP air stream 54 may bechanneled through more than one heat exchanger to facilitate optimizingthe use and recovery of thermal energy within stream 54. Afterextraction air 46 and compressed air 42 are combined into HP air stream54, a secondary stream 60 may be extracted from HP air stream 54 tofurther use/recover the thermal energy of stream 54. Alternatively,secondary air stream 60 is not extracted from HP air stream 54.

In the exemplary embodiment, diluent N₂ 58 is used within combustor 22.More specifically, the diluent N₂ 58 and a fuel, such as syngas 48, areeach channeled to combustor 22 for combustion therein. In oneembodiment, heated diluent N₂ 58 is mixed with fuel prior to beingchanneled into combustor 22. In the exemplary embodiment, ASU 18channels diluent N₂ 58 to combustor 22. More specifically, ASU 18channels the diluent N₂ 58 into compressor 28 to compress the N₂ 58.Diluent N₂ 58 is heated during the compression process. To further heatthe diluent N₂ 58, the N₂ 58 is channeled from compressor 28 throughfirst heat exchanger 32, wherein the thermal energy of HP air stream 54heats the N₂ 58 flowing therethrough. In one example, the diluent N₂ 58is heated to about 750° F., or more generally heated to a range betweenabout 700° F. and about 800° F., by HP air stream 54. As such, heated,compressed diluent N₂ 62 is channeled to combustor 22 for combustiontherein. After heating the diluent N₂ 58 within first heat exchanger 32,in the exemplary embodiment, HP air stream 54 is channeled to fourthheat exchanger 38 and/or ASU 18.

Secondary air stream 60 having approximately the same physicalproperties, such as pressure and/or temperature, as HP air stream 54 ischanneled to second heat exchanger 34. Water and/or low pressure (LP)steam 64 is channeled through second heat exchanger 34 to HRSG 26 togenerate superheated steam. As water and/or LP steam 64 is channeledthrough second heat exchanger 34, secondary air stream 60 heats waterand/or LP steam 64 to generate medium pressure (MP) steam 66. Morespecifically, the thermal energy contained in secondary air stream 60 isused to heat water and/or LP steam 64 and, thus, increase the pressurethereof In one example, when water 64 is supplied to second heatexchanger 34, water 64 is vaporized to a pressure between about 80 psito about 600 psi. Such steam is considered to be “medium pressure”steam. Such medium pressure steam is then superheated to a temperaturebetween about 600° F. and about 800° F. When LP steam 64 is supplied tosecond heat exchanger 34, LP steam 64 is supplied at a pressure ofbetween about 80 psi to about 150 psi and is superheated to atemperature between about 600° F. and about 800° F. After secondary airstream 60 generates MP steam 66, secondary air stream 60 is channeled tothird heat exchanger 36. Alternatively, secondary air stream 60 ischanneled to fourth heat exchanger 38 and/or ASU 18 without flowingthrough third heat exchanger 36.

In the exemplary embodiment, ASU 18 supplies high pressure oxygen (HPO₂) 68 to gasification unit 16 for use in the gasification processperformed therein. More specifically, within gasification unit 16 a fuel70, such as coal, biomass, a hydrocarbonaceous feed, and/or any othersuitable fuel, is combined with HP O₂ 68 to generate syngas 48 throughthe gasification process performed therein. Syngas 48 generated ischanneled to combustor 22 for combustion therein, as described herein.More specifically, in the exemplary embodiment, to generate HP O₂ 68,ASU 18 separates oxygen from air 56. Moreover, ASU 18 separates nitrogenfrom air to generate diluent N₂ 58. More specifically, ASU 18 receivescooled HP air stream 56 and generates HP O₂ 68 and diluent N₂ 58therefrom. HP O₂ 68 is channeled to gasification unit 16 and diluent N₂58 is channeled to combustor 22, as described herein.

HP O₂ 68 is channeled to gasification unit 16 via third heat exchanger36. Alternatively, HP O₂ 68 is channeled to gasification unit 16 withoutbeing channeled through third heat exchanger 36. In the exemplaryembodiment, within third heat exchanger 36, thermal energy remainingwithin secondary air stream 60, after stream 60 is discharged fromsecond heat exchanger 34, is used to heat HP O₂ 68. More specifically,as HP O₂ is channeled through third heat exchanger 36 heat istransferred from secondary air stream 60 to HP O₂ 68. HP O₂ 68 isdischarged from third heat exchanger 36 to gasification unit 16, andsecondary air stream 60 is returned to HP air stream 54. In analternative embodiment, rather than third heat exchanger 36 being usedto heat HP O₂ 68, third heat exchanger 36 is used to heat a water flowand/or a steam flow, such as a low pressure steam flow.

In the exemplary embodiment, the re-united HP air stream 54 is channeledthrough fourth heat exchanger 38. Alternatively, the re-united HP airstream 54 is channeled to ASU 18 without being channeled through fourthheat exchanger 38. In the exemplary embodiment, HP air stream 54 ischanneled through fourth heat exchanger 38 to heat a condensate 72generated in the steam cycle. More specifically, condensate 72 ischanneled through fourth heat exchanger 38, and thermal energy of HP airstream 54 is used to heat condensate 72. As such, heated condensate 74is returned to the steam cycle. In an alternative embodiment, a fluidflow other than condensate 72 is heated within fourth heat exchanger 38.In the exemplary embodiment, cooled, HP air stream 56 is discharged fromfourth heat exchanger 38 into ASU 18 for use in generating HP O₂ 68 anddiluent N₂ 58, as described herein.

Moreover, and as described herein, HP air stream 54 is split such thatone portion, about 60% to about 90% of stream 54, is used to heatdiluent N₂ 58, and the remaining portion, about 10% to about 40% ofstream 54, is used to heat steam 66 and HP O₂ 68. As such, the thermalenergy of the hot, HP air stream 54 is utilized to heat a plurality offluid flows within plant 10 as stream 54 cools. Accordingly, a largeportion, such as 85%, of thermal energy within stream 54 is recoveredand used to heat diluent N₂ 58, HP O₂ 68, and/or condensate 72, and/orto generate MP steam 66. The electrical equivalent of the thermal heatrecovered from stream 54 is significantly greater than the additionalpower required for adiabatic air compressor 30. As such, the overallefficiency of plant 10 is higher as compared to the overall efficiencyof the known IGCC power plants described above.

Additionally, the above-described power plant realizes an overallincreased heat efficiency as compared to power plants that includeintercooled compressors. More specifically, for a given air flow, anadiabatic compressor typically requires about 25% more compression powerthan an intercooled compressor requires. Although compressing airincreases the air temperature, the temperature of an air streamcompressed in an intercooled compressor is generally below about 200° F.As such, the thermal energy of air discharged from an intercooledcompressor is dissipated and/or reduced in a cooling tower, whichresults in additional power consumption in the cooling water circuit. Incontrast, air compressed in an adiabatic compressor is increased to apressure of between about 180 psig and about 250 psig, and a temperatureof between about 750° F. and about 850° F. Using the processes andsystems described herein, a large portion, such as more than 85%, of thethermal energy contained in the compressed air stream may be recoveredand advantageously used to facilitate heating nitrogen, oxygen, steamturbine condensate, and/or other process flows, and/or to produce mediumpressure steam. Accordingly, as would not be expected, using anadiabatic air compressor, such as compressor 30, facilitates increasinga power output of a steam turbine, such as steam turbine 14, and thus,increases a net power output and efficiency of an IGCC power plant, ascompared to a net power output of an IGCC power plant using anintercooled air compressor.

Further, the above-described processes and systems may be used with heatexchangers having tight approach temperatures. For example, suchprocesses and systems may be used with approach temperatures lower thanapproximately 30° F. Moreover, a nitrogen flow within an IGCC plant canbe heated to about 750° F. and, if necessary, an oxygen flow within theIGCC plant can also be heated to about 750° F. If the oxygen flow is notheated to approximately the same temperature as the nitrogen flow, amedium pressure steam flow may optionally be generated and/or thenitrogen may be used for regeneration of an ASU molecular sieve may beheated. When the nitrogen is heated, the efficiency of the nitrogenwithin the regeneration of the molecular sieves is facilitated to beincreased.

Exemplary embodiments of methods and systems for use with an integratedgasification combined cycle are described above in detail. The methodsand systems are not limited to the specific embodiments describedherein, but rather, components of the systems and/or steps of themethods may be utilized independently and separately from othercomponents and/or steps described herein. For example, the methods mayalso be used in combination with other heat recovery systems andmethods, and are not limited to practice with only the integratedgasification combined cycle system and method as described herein.Rather, the exemplary embodiment can be implemented and utilized inconnection with many other heat recovery applications.

Although specific features of various embodiments of the invention maybe shown in some drawings and not in others, this is for convenienceonly. In accordance with the principles of the invention, any feature ofa drawing may be referenced and/or claimed in combination with anyfeature of any other drawing.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. An integrated gasification combined cycle (IGCC)power plant comprising: an air separation unit configured to discharge anitrogen flow and an oxygen flow; a first heat exchanger coupled in flowcommunication with said air separation unit, said first heat exchangerconfigured to heat the discharged nitrogen flow; a second heat exchangercoupled in flow communication with said air separation unit, said secondheat exchanger configured to heat the discharged oxygen flow; a thirdheat exchanger coupled in flow communication with a steam cycle, saidthird heat exchanger configured to heat a condensate stream receivedfrom the steam cycle, and a first adiabatic air compressor coupled inflow communication with said first, second, and third heat exchangers,said first adiabatic air compressor configured to discharge a compressedair flow comprising a first flow and a second flow, wherein said firstflow is channeled to said first and third heat exchanger and said secondflow is channeled to said second and third heat exchanger.
 2. An IGCCpower plant in accordance with claim 1 further comprising a gasificationunit coupled in flow communication with said air separation unit, saidair separation unit configured to discharge said oxygen flow into saidgasification unit.
 3. An IGCC power plant in accordance with claim 1further comprising a gas turbine engine comprising a second adiabaticair compressor configured to discharge an extracted compressed heatedair flow into said compressed heated air flow.
 4. An IGCC power plant inaccordance with claim 1 further comprising a heat recovery steamgenerator coupled in flow communication with said third heat exchanger,said third heat exchanger configured to channel a heated condensatestream to said heat recovery steam generator.
 5. An IGCC power plant inaccordance with claim 1 further comprising a fourth heat exchangercoupled in flow communication with the steam cycle, said fourth heatexchanger configured to receive said second flow to heat a fluid streamwithin said fourth heat exchanger.
 6. An IGCC power plant in accordancewith claim 1 further comprising a compressor coupled in flowcommunication with said air separation unit, said compressor configuredto compress the discharged nitrogen flow.
 7. A steam generation systemcomprising: a first adiabatic air compressor for generating a firstcompressed air flow; a second adiabatic air compressor for generating asecond compressed air flow, wherein the second compressed air flow iscombined with the first compressed air flow to generate a combined airflow; a first heat exchanger configured to receive a first discreteportion of the combined air flow and a nitrogen flow; a second heatexchanger configured to receive a second discrete portion of thecombined air flow and an oxygen flow; and a steam generator coupled inflow communication with said first adiabatic air compressor and saidsecond adiabatic air compressor, wherein said first and secondcompressed air flows heat a condensate flow to generate steam withinsaid steam generator.
 8. A system in accordance with claim 7 furthercomprising a third heat exchanger coupled in flow communication withsaid first and second adiabatic air compressors, said third heatexchanger configured to use said first and second compressed air flow toheat a steam cycle condensate flow.
 9. A system in accordance with claim7 further comprising: a heat recovery steam generator coupled in flowcommunication with said steam generator; and a gas turbine engine thatcomprises said first adiabatic air compressor, said gas turbine enginein flow communication with said heat recovery steam generator, said gasturbine engine configured to discharged a heated fluid flow into saidheat recovery steam generator for generating steam therein.